1. Field of the Invention
The present invention relates to a maintenance control of an ink head unit in an ink circulation type inkjet printer.
2. Description of the Related Art
An inkjet printer is a printer that prints on sheets by ejecting ink from multiple nozzles provided on inkjet heads. If inkjet printer has not ejected ink for a long time, solvent is evaporated from the ink adhered mainly to the inkjet heads, and the viscosity of the adhered ink is increased. Then the printer is not able to show its true printing performance. Therefore, for the inkjet heads, maintenance is done in some methods such as ink suction and nozzle cleaning before printing when the printing is performed after a predetermined elapsed time from the last performance.
In general, all nozzles of inkjet heads are not necessarily used in each printing. For instance, FIG. 1A shows a color inkjet printer accepting A3 size sheets provided with an ink head unit 230 that includes line type inkjet heads 130K, 130C, 130M and 130Y for black ink, cyan ink, magenta ink and yellow ink, respectively. When the inkjet printer performs printing on an A4 size sheet in color, ink is not ejected from nozzles of areas “a1” and “a2” at both end portions of each inkjet head. Each of the inkjet heads 130K, 130C, 130M and 130Y has alternately-arranged six nozzle plates, each of which is provided with multiple nozzles. In other words, the six nozzle plates are arranged on each inkjet head in a zigzag matter.
In such a case, if a printing job requests for printing on an A3 size sheet in color, then the printer is not able to show its true printing performance even if the printing job is performed within a predetermined elapsed time from the last printing job. This is because the time that ink has not been ejected from the nozzles of the areas “a1” and “a2” is longer than the predetermined elapsed time, where these nozzles were not used in the last printing. Therefore, it is preferable that maintenance for the ink head unit 230 is done in view of such a situation.
In addition, as shown in FIG. 1B, when the above-mentioned inkjet printer performs printing on an A4 size sheet in black-and-white, ink is not ejected from the nozzles of whole area of the inkjet heads 130C, 130M and 130Y, and the nozzles at both end portions of the inkjet head 130K In FIG. 1B, the above-mentioned areas of the color inkjet heads and black inkjet head are collectively referred to as an area “a3” as a whole.
In such a case, if a printing job requests for printing on an A4 size sheet in color, then the printer is not able to show its true printing performance even if the printing job is performed within a predetermined elapsed time from the last printing job. This is because the time that ink has not been ejected from the nozzles of the area “a3” is longer than the predetermined elapsed time, where these nozzles were not used in the last printing. Therefore, it is preferable that maintenance for the ink head unit 230 is done in view of such a situation.
To address such issues, Japanese Patent Laid-Open Publication No. H11-192729 discloses a method to determine whether the size of a sheet to be printed in a printing job is the same as that in the last printing job, and to do maintenance for an ink head unit when the sheet size in the printing job is different from that in the last printing job. In addition, Japanese Patent Laid-Open Publication No. 2002-86754 discloses a method to do maintenance for an ink head unit when a printing job requests for printing in color while the last printing job requested for printing in black-and-white.
According to these technologies, maintenances is always done in some methods such as ink suction and nozzle cleaning even if a printing job is performed within a predetermined elapsed time from the last printing job when the present printing job requests for ejecting ink from unused nozzles of inkjet heads in the last printing job. However, these maintenance methods consume ink and require a substantial time to start printing. Therefore, it is preferable that excessive maintenance of the ink head unit is avoided.